For 2 years industry officials, states, and environmentalists have had 2 January 2011 circled on their calendars. That's the date greenhouse gases officially become regulated pollutants under the Clean Air Act—a direct result of a 2007 ruling by the U.S. Supreme Court that carbon dioxide is a pollutant under that law. The Environmental Protection Agency's effort to control greenhouse emissions will only get more controversial as myriad lawsuits challenge the regime and Republicans, now ascendant in the House of Representatives, seek to stop EPA in its tracks.

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Two things begin on Sunday, for the two main regulated sources of greenhouse gas pollution. One involves cars and light trucks, which are responsible for about one-fifth of U.S. heat-trapping emissions. The rules apply to 2012 model vehicles, which can be sold starting Sunday. They must now follow toughened CAFE fuel efficiency standards laid out in May. With industry on board—though there's some grumbling—these steps are relatively uncontroversial.

The more divisive efforts are for regulating power plants, refineries, and big factories which emit greenhouse gases. Starting Sunday, new facilities require a permit if they are expected to emit 75,000 tons of CO2 (or equivalent greenhouse gas) a year or if they are already running but plan to add that much new capacity. In July existing plants that emit 100,000 or more tons will need a permit.

State regulators, with oversight from EPA, serve to enforce the Clean Air Act for all polluters within their borders. In November, EPA released draft "guidance" for states in setting up their regulations for stationary big emitters. The guidance includes a mix of three strategies to cut pollution: using technology to make plants more efficient, switching to more efficient sources of energy (in most cases, from coal to natural gas), or capturing greenhouse gas emissions and storing them underground. (For coal plants, it's dubbed "Carbon Capture and Storage.")